where \(J_n\)  is a Bessel function of the first kind [1]}. We also note here that the function \(f\)  from Section  is
\(f(z) = \exp (\theta (2z+z^{-1})) = \exp (\theta \sqrt{2} (z \sqrt{2} + (z \sqrt{2})^{-1})) = \sum _{n \in \mathbb {Z}} (z \sqrt{2})^n I_n (2 \sqrt{2} \theta )\) 
